Core–shell anatase anode materials for sodium-ion batteries: the impact of oxygen vacancies and nitrogen-doped carbon coating†
In this work, the impact of oxygen vacancies and nitrogen-doped carbon coating on the sodium-ion storage properties of anatase TiO2 has been demonstrated. Oxygen vacancies and nitrogen-doped carbon coating were introduced simultaneously by the calcination of core–shell structured TiO2 spheres in a reducing atmosphere. Compared to the anatase TiO2 with and without oxygen vacancies, TiO2−x@NC exhibits much better electrochemical performance in the storage of sodium ions. A high reversible capacity of 245.6 mA h g−1 is maintained at 0.1 A g−1 after 200 cycles, and a high specific capacity of 155.6 mA h g−1 is achieved at a high rate of 5.0 A g−1. The significantly improved electrochemical performance of the core–shell structured anatase TiO2 spheres is attributed to the synergistic effect of the oxygen vacancies in the anatase lattice and surface nitrogen-doped carbon coating. This work provides an efficient strategy for improving the electrochemical performance of metal–oxide-based electrode materials for sodium-ion batteries.